Compare arrays as (multi-) sets

Question

I\'m looking for an efficient way to find out whether two arrays contain same amounts of equal elements (in the == sense), in any order:

foo = {         


        

Answer 1

You can implement the following algorithm:

• If a and b do not have the same length:
  • Return false.
• Otherwise:
  • Clone b,
  • For each item in a:
    • If the item exists in our clone of b:
      • Remove the item from our clone of b,
    • Otherwise:
      • Return false.
  • Return true.

With Javascript 1.6, you can use every() and indexOf() to write:

function sameElements(a, b)
{
    if (a.length != b.length) {
        return false;
    }
    var ourB = b.concat();
    return a.every(function(item) {
        var index = ourB.indexOf(item);
        if (index < 0) {
            return false;
        } else {
            ourB.splice(index, 1);
            return true;
        }
    });
}

Note this implementation does not completely fulfill your requirements because indexOf() uses strict equality (===) internally. If you really want non-strict equality (==), you will have to write an inner loop instead.